Organoaluminum-iron salt-bisarsine catalysts for use in preparing 1, 4-dienes



United States Patent 3,407,245 ORGANOALUMINUM-IRON SALT-BISARSINE CATALYSTS FOR USE IN PREPARING 1,4- DIENES Christos Sarafidis, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Dec. 15, 1967, Ser. No. 690,779 16 Claims. (Cl. 260-680) ABSTRACT OF THE DISCLOSURE A catalyst for use in preparing 1,4-dienes from ct-monoolefins and conjugated dienes. The catalyst is prepared by mixing an organoaluminum compound, an iron salt and a bisarsine in a liquid medium in any order, either in the presence of the monomers or separately. A process utilizing said catalysts for preparing 1,4-dienes from oc-monoolefins and conjugated dienes is also provided.

BACKGROUND OF THE INVENTION Alapha-olefin elastomers are of increasing importance today. Particularly valuable are the copolymers cont-aining sulfur-curable side-chain unsaturation resulting from incorporation of nonconjugated diene units. US. Patent 2,933,480 to Gresham et al. describes representative copolymers of this type. Nonconjugated dienes useful in making these copolymers include 1,4-hexadiene itself and derivatives wherein the monomer still has one terminal vinyl group, e.g., 4-methyl-1,4-hexadiene. Other 1,4-dienecontaining elastomers are also important, for example, the oopolymer prepared by copolymerizing isobutylene with 2-alkyl-l,4-hexadienes in the presence of a cationic catalyst, e.g., a Friedel-Crafts catalyst such as boron trifluoride or stannic chloride-Water.

Various catalysts are known for use in synthesizing 1,4- dienes fro-m u-monoolefins and conjugated dienes. French Patent 1,462,308 discloses making hexadiene from ethylene and 1,3-butadiene with a ferric chloride-bisphosphineorganoaluminum catalyst and Japanese patent publication 7,850/ 66 teaches the use of a ferrous chloride-monophosphine-dialkylaluminum chloride catalyst for the same reaction. The catalyst disclosed in these publications and others of a similar nature, while being somewhat effective in catalyzing the desired reaction, are sometimes deficient with respect to their activity and stereoselectivity, i.e., their use results in the production of substantial amounts of undesirable by-products in addition to the desired 1,4dienes.

Because of the great utility of aliphatic 1,4-dienes in making important elastomers, there has been a need for a catalyst system of high activity and ready availability which, when used in the reaction of conjugated dienes and a-rnonoolefins, produces the desired 1,4-dienes in good yield.

SUMMARY OF THE INVENTION According to this invention a catalyst for use in preparing 1,4-dienes is prepared by mixing an organoaluminum compound, an iron salt, and a bisarsine of the formula:

Q2 Q3 wherein each Q group is independently aryl, alkyl, cycloalkyl, aralkyl, alkaryl, or at least one of the pairs of Q groups Q -Q and Q -Q are joined together to form a saturated 5 or 6 membered ring, and R is ethylene, trimethylene or vinylene (CH=CH--). The invention also provides a process which utilizes said catalyst in preparing 1,4-dienes from a-monoolefins and conjugated dienes.

3,407,245 Patented Oct. 22, 1968 ice DETAILED DESCRIPTION Ethylene is the preferred monoolefin for use in the present invention, being commercially available in large quantities at a very low price and, importantly, capable of combining with a conjugated diene to give a 1,4-diene having a terminal carbon-carbon double bond well suited for the reaction with coordination catalysts. Other amonoolefins which can be used in this invention are those having the formula R-CH CH=CH where R is hydrogen, C -C alkyl or halogenated 0 -0 alkyl. Of this group the commercially available members having up to about 6 carbon atoms are preferred; propylene is the most preferred because of its availability and the importance of the dienes formed when it is used. A preferred example of the halogenated alpha-monoolefin is 5,6-dibromo-1-hexene. Other examples of hydrocarbons and halogenated hydrocarbon alpha-monoolefins suitable for use in the present invention are given in US. 'Patent 3,222,330 to Nyce et al.

The conjugated dienes which are used in this invention are those having the formula:

wherein each of the groups R and R is tolyl, halophenyl, phenyl, alkyl, hydrogen or R and R are joined together to form a cyclic diene containing up to 12 carbon atoms in the ring; each of R and R is alkyl or hydrogen and each of R and R is hydrogen, alkyl, aryl, alkaryl, aralkyl, or halo. The preferred conjugated diene for use in the present invention is 1,3-butadiene; it is commercially available in large quantities at an attractive price and when combined with ethylene, makes possible the preparation of 1,4-hexadiene which is a monomer particularly preferred for use in preparing sulfuracurable hydrocarbon elastomers by coordination catalysis. Other conjugated dienes which are useful in the present invention include isoprene, 1,3-pentadiene; 2,3-dimethyl-1,3-butadiene; 2,3- diohloro-1,3-butadiene; 1-phenyl-1,3-butadiene; Z-phenyl- 1,3-butadiene; l-p-tolyl-butadiene; 1,2-diphenyl-1,3-butadiene; 2,3-diphenyl-1,3-butadiene; 2-ethyl 1 phenyl-l,3- butadiene and l-p-chlorophenyl-1,3-butadiene.

Although the reaction of this invention in which 1,4- dienes are prepared involves the equimolecular addition of an alpha-monoolefin to a conjugated diene, it is not necessary to employ equimolar amounts of reactants. In typical batch operations the ratio of reactants can be continually changing. Both the alpha-monoolefin and the conjugated diene can be introduced into the reactor to establish a suitable value of the ratio before the reaction is initiated; thereafter additional alpha-monoolefin is fed therein during the course of the reaction until the desired conversion of the conjugated diene to the 1,4-diene is obtained. One or both of the reactants can be charged to the reaction vessel, continuously or intermittently during the reaction. In a preferred process, ethylene is maintained at practically a constant pressure over the diene (which is usually in solution as discussed hereinafter), until consumption of ethylene ceases. The proportions of reactants to be used in a given reaction may be routinely determined by one skilled in the art with reference to the example which follows:

The catalysts of this invention are prepared by mixing an organoaluminum compound, an iron salt and a bisarsine of the above-specified formula. A wide variety of organoaluminum compounds or mixtures thereof can be employed. Suitable classes include triorganoaluminums; organoaluminum halides such as diorganoaluminum monohalides, organoaluminum dihalides, and organoaluminum sesquihalides; diorganoaluminum hydrides and diorganoalum'inum alkoxides wherein the alkoxy group contains about 1-8 carbon atoms. The organic groups in the organoaluminum compounds include alkyl, aryl, aralykyl and alkaryl radicals and the halides are chloro, bromo or iodo.

The molecular weight of the organoaluminum compound is not critical; in general practice there is usually no practical advantage in employing compounds wherein the individual organic groups have more than 18 carbon atoms. The preferred compounds are the organoaluminum halides, diisobutylalurninum monochloride being particularly preferred because of the fast rate of reaction which it induces and its availability. Of the triorganoaluminum's used, triisobutylaluminum is preferred for the same reasons. Isobutylaluminum dichloride and ethylaluminum sesquihalide are also particularly useful in this invention. Other useful representative organometal compounds include: tri-n-butylaluminum; diethylaluminum bromide; isobutylaluminum dibromide; diisopropylaluminum monochloride; di-n-hexylaluminum monochloride; di-n-amylchloroaluminum; isopropylaluminum dichloride; triphenylaluminum; diphenylaluminum monochloride; bis(p-tolyl)aluminum monochloride; bis(p-chlorophenyl)aluminum monochloride; bis(3,4-dichlorophenyl) aluminum monochloride; bis(p fiuorophenyl)aluminum monochloride; dibenzylalurninum monochloride; and polymeric organoaluminums such as aluminum isoprenyl. Similar compounds containing condensed aromatic rings such as diisobutylnaphthylaluminum are also suitable.

In preparing the catalyst, the organoaluminum compound is utilized in amounts such that there is at least 1 gram-atom of aluminum for each gram-atom of iron in the catalyst. Greater amounts of aluminum up to 200 gram-atoms or more per gram-atom of iron can be used but are not economical. The amounts of aluminum Within this range to be used in order to form effective catalysts will vary with the iron salt employed, but can be routinely determined by one skilled in the art. A preferred general ratio is about -15 gram-atoms of aluminum per gram-atom of iron. Aluminum present in this quantity is commercially feasible and gives excellent reaction rates.

A wide variety of iron salts can be used in this invention including those containing the iron atom in the (II) or (III) valence state. Representative examples are iron tris(acetylacetonate), iron bis(acetylacetonate), iron (II) chloride (FeCl iron (II) bromide (FeBr iron (11) iodide (Fel and iron (II) diacetate. Preferred iron salts are iron (III) acetylacetonate and iron (III) chloride because of their high activity and ready availability.

The bisarsine,

is a necessary component of the catalyst along with the iron salt and organoaluminum' compound. The R group of this formula is ethylene (CH CH trimethylene (CH CH -CH or vinylene (CH=CH). The Q groups are C6-C15 aryl, C C alkyl, C4-C8 Cycloalkyl, C C aralkyl, C -C alkaryl or the pairs of Q groups, Q -Q and/or Q Q are joined together to form a saturated 5 or 6 membered ring, said ring containing one of the arsenic atoms indicated in the formula and the remaining members being carbon atoms.

The bisarsines useful in this invention can be made by the general procedures described in Advances in Organometallic Chemistry, vol. 4, ed. by F. G. A. Stone and R. West, Academic Press, New York, 1966, the section by W. R. Cullen entitled Organoarsenic Chemistry (pp. 145-242). Suitable information can also be found in Die Chemie der Metall-Organischen Verbinungen by E. Krause and A. von Grosse, Borntraeger, Berlin, 1937. Catalysts of particularly good performance are formed when all of the Q groups are phenyl. The preferred compound is ethylenebis[diphenylarsine]; detailed illustrations of its use are given in the example. Other repre- .4 sentative bisarsines includes: ethylenebis[ethyl phenylarsine]; ethylenebis [methyl phenylarsine]; ethylenebis [butyl phenylarsiue]; ethylenebis[benzyl phenylarsine]; ethylenebis [dibenzylarsine]; ethylenebis [dicycloliexylarsine] ethylenebis [diethylarsine]; ethylenebis [dihexylarsine]; trimethylenebis [diphcnylarsine]; vinylenebis [diphenylarsine]; ethylenebis[tolyl phenylarsine]; ethylenebis[diphenylylarsine] and ethylenebis[dinaphthylarsine]. The proportions are selected such that at least 0.5 grammole of bisarsine is present for every gram-atom of iron. The preferred ratios of gram-moles bisarsine:gram-atorns iron are in the range 0.5-2:1; catalysts so formed have high activities and form a minimum of by-products. Since the bisarsine is the most expensive component of the catalysts, higher proportions than 2:1 are ordinarily not used, the upper limit being dictated by economics.

The catalyst components are usually mixed together in a liquid solvent but can be mixed in the absence of any solvent. The hereinafter-described inert organic diluents in which the reaction is carried out are suitable solvents for the catalyst components. The components can be mixed separately or in situ in the presence of the monomer reactants. The order is not critical and allows for a variety of procedures to be used at the convenience of one skilled in the art. To avoid undesirable side reactions however, it is preferred that the iron compound and the bisarsine be brought together before the organoaluminum compound and both of the reactants are present. When this procedure is followed, the organoaluminum is added to the other two catalyst components before or after the alpha-monoolefin and the diene are prescut.

The preparation of the catalyst and its use in effecting the formation of 1,4-dienes from alpha-olefins and conjugated dienes can be carried out over a wide range of temperatures. Values varying from about 25 C. to about 150 C. can be used. At temperatures below about C. the rate may be too slow for operating convenience. The preferred temperature range lies between 80 and 120 C., about -100 C. being particularly preferred for practical operation and good rates of reaction.

The proportion of the catalyst in the monomer reaction zone can be varied widely. For economic reasons, it is desirable to use as little catalyst as possible consistent with a reasonable reaction rate; a lower limit being at least about .001 millimole of the iron compound per mole of diene used. Typical proportions are illustrated by the example which follows, though proportions outside these ranges can be employed, if desired. Those skilled in the art can determine the optimum amount of a particular catalyst for a particular set of monomers by routine experiments.

The pressure employed will vary with the volatility of the monomers, the inert medium used and the reaction temperatures selected. A practical range of pressures for generally available reactors is from about 1 atmosphere absolute to about 2000 p.s.i.g. In order to operate at temperatures at which product formation takes place at a convenient rate, it may be necessary to maintain superatmospheric pressure to liquify the diene.

The reaction is usually carried out in an inert organic diluent. By inert it is meant that the diluent will not deactivate the catalyst; thus it does not contain groups bearing Zerewitinolf-active hydrogen atoms, for example, hydroxyl groups, carboxyl groups, and the like and it is free from impurities such as alcohol and water bearing these substituents. Oxygen and carbon monoxide should also be excluded. For optimum yields, the diluent should not undergo side reactions with the catalyst, the monomers, or the 1,4-diene products. Purification of the diluent and monomers can be carried out by the procedures familiar to those skilled in the art of coordination catalysis where organometal compounds are involved. If it is desired to isolate the 1,4-diene from the reaction mixture, it is preferable that the diluent be easily separable;

the boiling point of thediluent should thus be different enough fromthat of the diene productto afford convenient fractionation. Representative 'suitablediluents inelude: tetrachloroethylene, methylene chloride,,..chlorobenzene, aromatic hydrocarbons such as benzene 'and'toluene; and aliphatic and'cycloaliphatic hydrocarbons such as hexane and decalin respectively. It is believed that any diluent useful for conducting the coordination catalyzed polymerization of hydrocarbon monomers'can be used here. The conjugated diene itself, for' example'1,3-butadiene, can serve as the diluent.

The 1,4-diene can be prepared by the process of the present invention in a batch reactor or in a continuous reactor. The reaction time is selected to carry out the desired conversion of 1,4-diene and can vary widely. Op- I tionally, the reaction is stopped by adding a minimal amount of Zerewitinoff-active hyrogen compound, frequently a low molecular weight alcohol such as isopropanol, to deactivate the catalyst. After the reaction has stopped, the gases are left off and the liquid directly distilled, the 1,4-diene being separated by fractionation. Representative separation procedures are givenf in the exaluminum compound in milliliters of solvent is added. In Example 1 where the catalyst is preformed, the solution of catalyst in 50 milliliters of solvent is added through the catalyst injection tubes at the desired reaction temperature and pressure.

As'the reaction proceeds, ethylene is supplied on demand. At the end, the catalyst is deactivated by injection of one to two milliliters of isopropanol. Gases are then vented off. The 1,4-hexadiene content of the residual liquid is determined by gas chromatography.

In Example I the catalyst is preformed by adding 10 millimoles of neat diisobutylaluminum monochloride to a solution of l millimole of ferric chloride and 2 millimoles of ethylenebis(diphenylarsine) in 50 milliliters of chlorobenzene at room temperature. The preformed catalyst thus obtained is aged at room temperature for about 124 minutes before being used.

Results of the 1,4,.-hexadiene syntheses are indicated in the'table which follows: The results indicate that use of the catalysts of this invention results in good yields of cis-l,4-hexadiene produced in relatively short reaction times.

TABLE..PREPARATION OF CIS-1,4-HEXADIENE FROM ETHYLENE AND 1,3-BUTADIENE 1,3-BD Solvent Temp. Press. Time Cls-1,4-HD Ex. Fe salt; (IAS)1(CH1)I1 Al compound (g.) (ml.) C.) (p.s.i.g.) (min) pro(du)ced l F8013, 1 mmole... n=2, 2 mmoles DIBAC,10 mrnoles 86 01, 600. 95-100 99-107 142 54. 3 2 Fe(Ac.%c);, 1 n=2, 1 mmole ..do 81 Cl, 500 94-99 99-105 69 22 mmo e. 3 FeBn, 1 mmole do DIBAC,5mmoles v 61 o 01, 500.... 9697 100102 162 20,4. 4 FeCl;, 1 mmole n=2, 2 mmoles 'IIBA, 10 mmoles 78 4: CH3, 600.. 85-97 119121 198 24. 1

TIBA (tsobutyl) 3A1. AcAe acetylacetonate.

BD =butadiene.

'amples which follow. The reaction mixture which con- EXAMPLES 1-4 In these examples, four experiments are carried out to illustrate the preparation of cis-l,4-hexadiene from ethylene and 1,3-butadiene. The reactions are carried out in a 1.9-liter stainless steel pressure reactor fitted with a mechanical stirrer, two gas inlet tubes, two pressure funnels for injection of catalyst solutions, a port for the charging of solids (e.g. iron salts, bisarsines), a 10-milliliter tube for the taking of samples while the reactor is under pressure, a rupture disc, a thermocouple well, and an outlet leading through an overflow bomb to a backpres'sure regulator. The back-pressure regulator is set to vent at pressures p.s.i.g. above the operating pressure specified in the table below.

The following purification precautions are taken: Ethylene is passed through a molecular sieve column prior to entry into the reactor. 1,3-butadiene is passed through another molecular sieve, added to a SOO-milliliter stainless steel cylinder for weighing, and transferred from there to the reactor in the vapor phase with cooling of the reactor by a mixture of crushed solid carbon dioxide and acetone. The solvent is dried and deoxygenated before use.

After the reactor has been flushed with nitrogen, it is charged with solvent andin Examples 2-4 where the catalyst is not preformed-with the iron salt and bisarsine. The reactor is cooled and charged with butadiene. When the reactor has subsequently been heated to the temperature called for in the table below, ethylene is added up to the desired pressure. Then a solution of the organo- HD =hexadiene.

an organoaluminum compound and a bisarsine having the formula:

wherein each Q group is independently C C aryl, C C alkyl, C -C cycloalkyl, C -C aralkyl, C7-C13 alkaryl or at least one of the pairs Q -Q and Q -5Q is joined together to form a saturated 5 or 6 membercd ring, said ring containing the arsenic atom and the remaining members being carbon atoms, and R is ethylene, trimethylene, or vinylene; said components being mixed in such proportions that there is at least 0.5 gram-mole of bisarsine per gram-atom of iron and at least 1 gramatom of aluminum per gram-atom of iron.

2. The catalyst of claim 1 wherein the iron salt is iron (III) acetylacetonate, iron (II) acetylacetonate, iron (III) chloride, iron (II) chloride, iron (II) bromide, iron (II)v iodide or iron (II) acetate and the bisarsines are ethylenebis[diphenylarsine]; ethylenebis [ethyl phenylarsine] ethylenebis [methyl phenylarsine] ethylenebis[butyl phenylarsine]; ethylenebis[benzyl phenylarsine]; ethylenebis[dibenzylarsine] ethylenebis [dicyclohexylarsine] ethylenebis [diethylarsine] ethylenebis[di-n-hexylarsine] trimethylenebis[diphenylarsine] vinylenebis [diphenylarsine] ethylenebis[tolyl phenylarsine]; ethylenebis[diphenylylarsine] or ethylenebis [naphthylarsine] 3. The catalyst of claim 2 wherein the organoaluminum compound is at least one from the group consisting of triorganoaluminums, diorganoaluminum monohalides;

organoaluminum dihalides; organoaluminum sesqui halides; diorganoaluminum hydrides or diorganoaluminum alkoxides, wherein the organo groups are C C 'alkyl, C C aryl, C -C1 alkaryl, or C C aralkyl; the halides are chloride, bromide or iodide and the alkoxy groups are C -C 4. The catalyst of claim 3 wherein the organoaluminum compound is at least one of triisobutylaluminum, diisobutylaluminum monohalide, diethylaluminum halide, isobutylaluminum dihalide, or ethylaluminum sesquihalide, wherein the halide is chloride, bromide or iodide.

5. The catalyst of claim 3 wherein the bisarsine is ethylenebis [diphenylarsine] trimethylenebis [diphenylarsine] or vinylenebis[diphenylarsine].

6. The catalyst of claim 5 wherein the organoaluminum compound is at least one of triisobutylaluminum, diisobutylaluminum monohalide, diethylaluminum halide, isobutylaluminum dihalide, or ethylaluminum sesquihalide, wherein the halide is chloride, bromide or iodide.

7. The catalyst of claim 6 wherein the bisarsine is ethylenebis[diphenylarsine] and the organoaluminum compound is diisobutylaluminum chloride, or triisobutylaluminum.

8. The catalyst of claim 7 wherein the iron salt is iron (III) acetylacetonate, or iron (III) chloride and the organoaluminum compound is diisobutylaluminum chloride.

9. The catalyst of claim 8 wherein the components are present in proportions such that there is 0.5-2.0 grammoles of bisarine per gram-atom of iron and 5-15 gramatoms of aluminum per gram-atom of iron.

10. In a process for the preparation of an aliphatic 1,4-diene which comprises reacting, in the presence of a catalyst, an a-monoolefin with a conjugated diene; the improvement which comprises using as the catalyst the product of claim 1.

11. In a process for the preparation of an aliphatic 1,4-diene which comprises reacting, in the presence of a catalyst, an a-monoolefin with a conjugated diene; the improvement which comprises using as the catalyst the product of claim 3.

12. The process of claim 11 wherein the a-monoolefin 5 is ethylene or propylene and the conjugated diene is 1,3-

butadiene, 2 methyl 1,3 butadiene, 1,3 pentadiene or 2,3-dimethyl-1,3-butadiene.

13. The process of claim 11 wherein the u-monoolefin is ethylene and the conjugated diene is 1,3-butadiene.

14. The process for the preparation of an aliphatic 1,4-diene which comprises reacting, in the presence of a catalyst, an e-monoolefin with a conjugated diene; the improvement which comprises using as the catalyst the product of claim 7.

15. The process of claim 14 wherein the a-monoolefin is ethylene and the conjugated diene is 1,3-butadiene.

16. vIn a process for the preparation of 1,4-hexadiene comprising reacting ethylene and 1,3-butadiene in the presence of a catalyst, the improvement which comprises using as the catalyst the product of claim 9 in an amount such that there is at least about .001 millirnole of the iron salt per mole of conjugated diene.

References Cited UNITED STATES PATENTS 3/1967 Hata et al 260-680 PAUL M. COUGHLAN, JR., Primary Examiner. 

